Recently, acceleration sensors having a movable structural portion and utilizing gravity acceleration to detect inclined displacement of an apparatus or the like have been developed. Such an acceleration sensor generally utilizes piezoresistance effect of a semiconductor. For example, a cavity portion is formed within a silicon substrate to accommodate therein a block-shaped movable structural portion freely movable in three-dimensional directions. The movable structural portion is coupled to the silicon substrate with a beam which is a bridge structure, and is arranged such that stress corresponding to the movement of the movable structural portion is applied to a piezo element. Then, a change in the stress applied to the piezo element is detected as a change in resistance. Instead of the piezo element, a capacitive element provided in the movable structural portion can be used as an element for detecting the displacement.